safe original png-compression
I use
to (imho lossless) compress PNG-images.
However if I resave it in Gimp it almost always increases file-size, even with the strongest compression, even if I simplify the image (remove black dots/dust from scan or I remove alpha-channel, crop, ...)
The suggestion is the PNG-analogy similar to @Jehan 's comment to keep the JPEG representation around in memory. So the original PNG-compression should be tried on resave if it is smaller to the Gimp-suggested one.